Mitochondria supply energy for cellular function while their dysfunction causes cell death. Endoplasmic reticulum (ER) mediates protein synthesis and folding and its dysfunction causes ER stress and protein aggregation. Autophagy is activated to clean up defective mitochondria and protein aggregates (aggresomes) through lysosomes to maintain mitochondrial homeostasis and relieve ER stress. Autophagic dysfunction induces oxidative stress that causes DNA double strand breaks and the generation of aneuploidy cells leading to cancers. We discovered that C19ORF5 regulates general autophagy and mitotic mitophagy in collaboration with tumor suppressor RASSF1A-mediated microtubular dynamics and overall autophagic activity via Bcl-2/XL protein-controlled canonical and noncanonical autophagic pathways. We predict that C19ORF5 inhibits the generation of aneuploidy to prevent cancer at its origin and impedes further karyotype evolution that underlies cancer's variability and relapse after therapy. To test the hypothesis, specific aims are designed to characterize (1) the mechanism by which C19ORF5 regulates autophagy, and (2) the mechanism by which C19ORF5 suppresses tumorigenesis through autophagic regulation. The experimental approach will use C19ORF5 knockout mice carrying a transgenic autophagic marker GFP-LC3 and their primary hepatocyte cultures as models for biochemical, cell biological and cancer biological studies. The ultimate goal is to understand the general mechanism of tumor suppression and develop strategies to prevent cancers at their origin and terminate cancer relapse after therapy in general using the hepatoma as a prototype. PUBLIC HEALTH RELEVANCE: It is estimated that about half of ageing-related human diseases are caused by accumulation of cellular garbage due to dysfunction in mechanisms for cleaning up mis-folded/aggregated proteins and worn-out dysfunctional organelles. Autophagy, mitophagy when applied to mitochondria, maintains a healthy population of mitochondria and eliminates the toxic macromolecular waste so that oxidative stress-induced genomic instability is prevented. C19ORF5 regulates autophagy in general and mitophagy in particular and prevents tumorigenesis. The new knowledge will eventually lead to develop strategies to terminate cancer at its earliest origin, sensitize human cancers to radiation treatment and chemotherapy, and prevent tumor re-growth and disease recurrence.